[111.05] Repeating and Galactic Anisotropy of Gamma-Ray Bursts in Light of the BATSE 2B Catalogue

D.~Q.~Lamb, J.~M.~Quashnock (U.~Chicago)

Last year we reported evidence that ``classical'' gamma-ray bursts
repeat and that medium brightness bursts are concentrated
toward the Galactic center and in the Galactic plane
(Quashnock and Lamb 1993a,b),
based on analysis of the BATSE 1B catalogue (Fishman et al. 1994).
Here we examine this evidence in light of the BATSE 2B catalogue.
We take into account that the failure of on-board tape recorders
led to a $\sim 1/3$ decrease in the efficiency of burst detection
in the 2B-1B catalogue (comprising the 323 bursts in the 2B
catalogue that were detected after
the end of the 1B observing period).
We find that the distributions of
peak counts, peak flux, fluence and positional
errors of the 2B-1B bursts differ significantly
from those of the 1B.
Assuming that the 262 bursts detected in the 1B catalogue form a fair sample,
we simulate what would be expected in the 2B-1B and 2B catalogues.
We show that repeating is not detectable,
due to the lower detection efficiency and the
lack of detection of long duration, low peak flux bursts in the 2B-1B
observing period.
We also discuss the impact of these selection effects on the ability
to detect Galactic dipole and quadrupole moments.
We expect that the 3B-2B catalogue
will be as good as or better than the 1B catalogue,
and should offer a fair test of our claims of repeating and Galactic
anisotropy.

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This work was supported in part by NASA Grants NAGW 830,
NAGW 1284, NAG 5-1454, and NAG 5-2660.